OLYMPIA — U.S. Rep. Jay Inslee will launch a campaign for Washington governor early next week, wading back into state politics after more than a decade in Congress, a Democrat familiar with his plans said Thursday.

Inslee plans to make his announcement in Seattle, according to the person who spoke on condition of anonymity because Inslee’s plans have not been officially made public. He has long been positioning himself as a potential candidate, and that pathway cleared earlier this month when Gov. Chris Gregoire announced that she would not seek a third term.

Attorney General Rob McKenna has already declared his candidacy for the Republican nomination.

Inslee has represented Washington’s 1st Congressional District since 1999, covering northern suburbs of Seattle. He’s been a leader in Congress on battling climate change and promoting clean-energy alternatives, writing a book on the topic and touting the economic benefits of such a transition.

This won’t be Inslee’s first run for governor. After serving one term in Congress in the early 1990s, he lost in a rematch to current 4th District Rep. Doc Hastings in the Republican wave of 1994. He then sought the Democratic nomination for governor in 1996 but lost to Gary Locke, who went on to serve two terms.

Inslee already has signaled one key area where he plans to confront McKenna: He launched an online petition urging McKenna to drop his lawsuit against President Barack Obama’s health care overhaul. McKenna signed on to a multistate challenge of the law, arguing that it is unconstitutional because of a requirement that individuals without health insurance must purchase private insurance or face a fine.

Inslee said that McKenna’s support for the lawsuit indicated that he was trying to build support among “right-wing extremists.”

“With Washington state’s health care at risk, does Rob McKenna protect our interests, or his own?” Inslee said in a letter to supporters earlier this year.